In a communicating apparatus, for example, a Doherty amplifier is conventionally used to amplify high-frequency signals. With respect to efficiency characteristics in terms of output power of the Doherty amplifier, peak points of efficiency exist at an intermediate point and a maximum point of output power. For example, in the Doherty amplifier, if drain voltage of a carrier amplifier changes, the output power of the peak point varies, and if drain voltage of a peak amplifier changes, the output power of the maximum point varies.
In the Doherty amplifier, for example, the drain voltage of the carrier amplifier is set based on the average power of input signals and the drain voltage of the peak amplifier is set based on the peak power of input signals (see, e.g., Japanese Laid-Open Patent Publication No. 2010-114539). If a modulation mode or a signal multiplex mode (e.g., the number of carriers) of a transmission signal changes, a peak-to-average power ratio (PARK) varies. Therefore, efficiency characteristics for output power in the Doherty amplifier have to be controlled according to the properties of the signals.
However, since voltage is controlled based on the average power of the input signals in the conventional technique described above, the properties of the input signals are not reflected in the control of the voltage and the efficiency of amplification may not be controlled accurately.